Flexible articles such as tubing and sheeting, particularly those used in medical applications, can be made from a number of materials.
U.S. Pat. No. 3,796,775, while not teaching medical utility, does teach that molded articles such as tubing can be made from a composition having environmental stress-crack resistance and low-temperature impact strength. The composition taught is a homogeneous mixture of polyethylene, polyisobutylene or an ethylene/vinyl acetate copolymer, and N,N'-disteroylethylenediamine (N,N'-ethylene-bis-stearamide).
U.S. Pat. No. 4,198,983 teaches catheters made from a block copolymer having thermoplastic rubber characteristics with a central rubbery polyolefin block and terminal blocks of polystyrene and, optionally, cross-linked organic silicone and polypropylene. A hydrophobic oil-type plasticizer is added to provide softness. It teaches that in certain circumstances, cured silicone elastomers and fatty acid amides, together, provide reduced surface friction over that contributed by either ingredient alone.
U.S. Pat. No. 3,865,776 teaches kink-resistant tubing having a useful degree of clarity that is a combination of two types of block polymers, mineral white oil, high-melt-flow polypropylene and a resin. Each of the two block pollers has at least two monoalkenylarene and at least one substantially completely hydrogenated conjugated diene polymer block. They differ in molecular weight and monoalkenylarene polymer block content. The resin serves as a flow promoter and is compatible with either the monoalkenylarene or the diene polymer blocks. Examples of useful resins are ethylene/vinyl acetate copolymer and a copolymer of vinyl toluene and alpha-methylstyrene.
Non-cross-linked thermoplastics, especially polyvinyl chloride (PVC) containing large amounts of plasticizer, have found acceptance in a number of medical applications. PVC has, in deed, become the material of choice particularly for applications where transparency is required such as in respirator tubing. This is because its properties generally far exceed those needed for the various medical applications and it is inexpensive. Properties generally desired in medical tubing and sheeting applications where PVC has found utility are clarity or transparency (low haze), flexibility (drape), kink resistance, adequate burst strength, low surface tackiness, scratch resistance, and bondability to connectors.
Japanese Patent Publication J5-8050965 discloses a resin that has excellent transparency, softness, and resiliency and is therefore applicable to the manufacture of medical instruments such as catheters, blood bags and tubes. The resin employs vinyl-chloride-based resins blended with ethylene/vinyl acetate/carbon monoxide copolymer, low molecular weight plasticizers such as dioctyl phthalate, magnesium or calcium oxide, stabilizers such as calcium stearate and a bisamide.
Japanese Patent Application J5-9199749 discloses a somewhat similar resin for use in blood bags, tubes and the like. It is an ethylene-vinyl acetate/vinyl chloride graft copolymer blended with dicarboxylic acid amide. Surface stickiness is reported as being greatly reduced by the acid amide. Calcium-zinc stabilizers and epoxidized soybean oil are used with the graft copolymer and acid amide in the example.
While PVC has been preferred over other known polymers in many medical applications, PVC does present some problems. There is concern over possible health risks from plasticizers such as the dioctyl phthalate typically used in PVC. Environmentally, chlorine containing polymers are undesirable. With increased concern over disposal of medical waste, many hospitals now incinerate waste containing PVC. The corrosive incineration products that result must be handled. Many existing incinerators are not equipped with adequate scrubbers and are not made of adequately corrosion-resistant material.
What is needed, then, is a replacement for PVC that does not pose the environmental concerns of PVC, does not produce corrosive incineration products (does not contain chlorine) and does not require the addition of potentially hazardous plasticizers to obtain the properties desired. It must at the same time have properties sufficiently close to those of PVC to satisfy the needs of the medical community for clarity or transparency (low haze), flexibility (drape), kink resistance, adequate burst strength, low surface tackiness, scratch resistance, and bondability to connectors.
Multi-layer tubing and sheeting has now been found that can achieve the balance of properties needed, but these are difficult to manufacture and are relatively expensive. Coextrusion requires special equipment and bonding the layers together can be difficult. Recycle problems are presented when layers are made of different materials. Separating the components is difficult, and chipping them together is not practical, unless there is a use for the blend of components. Thus, the tubing or sheeting should preferably be of a single layer construction. It should be easily processible, preferably on the same equipment (molding, extrusion, assembly equipment and the like) as the PVC it replaces.
Ethylene copolymers have good flexibility without the need for plasticizers due to the nature of their polymeric structure. They have low crystallinity because of high levels of comonomer. They are, however very tacky and, thus, present handling problems.
Tackiness in some polymers can be reduced by incorporating certain antiblocking or "slip" agents into the polymer. These slip agents exude to the surface and reduce tackiness. Many types of slip agents are known. They include fatty acids or fatty acid derivatives such as esters, alcohols, metallic salts and amides. There is a vast range of primary amides, primary bisamides, secondary amides and secondary bisamides derived from saturated or unsaturated mono or diacids and amines. Modern Plastics Encyclopaedia lists many such materials.
With respect to ethylene copolymers, slip agents have found principal utility in reducing blocking tendencies in pellets and in thin films, particularly for packaging. On exudation, they are known to cause chalkiness, haze and loss of transparency.
U.S. Pat. No. 32,325 teaches incorporating 0.01 to 1 wt. % of a di-secondary bisamide selected from N,N'-ethylene-bis-oleamide; N,N'-ethylene-bis-erucamide; N,N'-dioleyl adipamide; and N,N'-dierucyl adipamide in a wide range of ethylene copolymer pellets. Flexibility, transparency and other properties desired in the present invention are neither taught nor suggested for the pellets or products made therefrom.
U.S. Pat. No. 3,821,179 teaches incorporating 0.05 to 2 wt. % N,N'-dierucyl adipamide or N,N'-dierucyl sebacamide as a slip agent in thin films and coatings of ethylene copolymer ionomer. Ethylene bipolymer ionomer films up to 2 mil (0.002 inches) thick are described. Only the above two agents are taught as suitable for reducing blockiness while still maintaining low chalking and good optical properties. Exudation of slip agent to the surface of these thin films is sufficiently rapid to provide reduced blocking. There is no suggestion of use in articles having thicker cross-section and no suggestion that the balance of properties needed for medical applications can be achieved.